The present invention relates to integrated circuit technology. More particularly, the present invention relates to user-programmable integrated circuits and to a configuration memory cell for programming such integrated circuits.
Numerous technologies are available for configuration memory cells for programming user-programmable integrated circuits. Both dynamic (SRAM type) and static (NVM type) memory cells are known.
In particular, resistive random-access memory (ReRAM) devices have been proposed for use in configuration memories for user-programmable integrated circuits such as field programmable gate array (FPGA) integrated circuits. One example is found in US Patent Application Publication S/N 2017/0179959 published Jun. 22, 2017 to the present applicant. ReRAM devices employ a solid electrolyte material disposed between two conductive electrodes. One of the conductive electrodes serves as a metal ion source. Initially, only a high-impedance path (on the order of >1 GΩ) exists between the two conductive electrodes. The ReRAM device is programmed by applying a sufficient potential of a first polarity across the ReRAM device, causing metal ions from the ion source conductive electrode to migrate into the solid electrolyte layer and form a conductive path between the two conductive electrodes. The ReRAM device is erased to return it to its high-impedance state by applying a sufficient potential of a second polarity, opposite the first polarity, across the ReRAM device, causing metal ions in the conductive path to migrate back to the ion source and remove the conductive path between the two conductive electrodes.
Unfortunately, ReRAM devices may be faulty, or become stuck in one of the two states, or even enter into an intermediate state. The arrangement of the prior art requires an option to provide redundancy of the entire cell in order to ensure proper operation in face of this possibility.